1. Field of the Invention
The present invention relates to a motor drive controller capable of controlling rotary driving of a motor having coils of plural phases and an image forming apparatus incorporating the motor drive controller.
2. Discussion of the Background Art
In various fields, such as home appliances, office instruments, car electric generators, etc., non-brush motors are widely used. For example, a non-brush motor having coils of three phases arranged at phase intervals of 120 degrees is known that is equipped with a position detector to output positional signals that represent positions of a rotor by changing a signal level at every electrical angle of 60 degrees, and witch employs rectangular wave driving that sends a particular rectangular wave current to a prescribed phase through an electrical angle of 120 degrees in accordance with the positional signal. The position detector generally includes three hall ICs, arranged so that the signal level of a positional change signal changes at every electrical angle of 60 degrees.
As a system to resolve problems of noise and vibration caused in rectangular wave driving, a sine wave driving system is known in that a sine wave current is flown through three-phase coils to rotate and drive a rotor in accordance with a position of the magnetic rotor. However, in order to flow the sine wave current, the rotational position of the magnetic rotor needs to be detected with a high resolution. Thus, a high-resolution encoder is necessarily arranged on a rotation shaft of the motor, thereby increasing cost.
By contrast, an inverter system described in Japanese Patent No. 3500328 includes a position detector that detects and outputs a cyclically changing positional signal in accordance with a position of a rotor, a pulse generation circuit that generates clock pulses having a frequency multiplied in accordance with a cycle of change in the positional signal, and a phase presumption circuit that counts clock pulses with reference to a changing point of the positional signal and predicts a rotational position of the magnetic rotor. Japanese Patent No. 3500328 further includes an inverter circuit that outputs a sine wave current in accordance with the predicted rotation phase. Thus, the non-brush motor is controlled by the sine wave driving system suppressing noise and vibration while omitting the expensive high-resolution encoder.
However, a position detector, such as a Hall IC, etc., constituting the position detector is susceptible to error in positioning due to reflow mounting onto a print substrate. If a changing point of the positional signal is erroneous due to the arrangement error of the position detector, a changing cycle of the positional signal is also erroneous. Thus, when a difference of a positional signal changing cycle varies per cycle, a difference of a frequency of clock pulses also varies when generated per cycle of the phase signal. Accordingly, when it is generated using such pulses, the sine wave discontinuously deforms or distorts, thereby likely causing unevenness of rotation and noise.
Japanese Patent Application Laid Open No. 2008-236831 (JP-2008-236831-A) proposes a motor drive control apparatus that includes a position detector that detects and outputs a cyclically changing positional signal in accordance with a position of a rotor, an absolute phase information outputting device that smoothens the positional signal and outputs absolute phase information based on the positional signal, and an inverter circuit that outputs a sine wave current in accordance with the absolute phase information. Specifically, the non-brush motor is controlled by the sine wave driving system suppressing noise and vibration while reducing the impact of any error occurring at the changing point of the positional signal due to arrangement error of the position detector.
However, since the motor control apparatus of JP-2008-236831-A generates the absolute phase information of the magnetic rotor by smoothening the difference of the positional signal caused by the arrangement error of the position detector (e.g. a hall IC), the impact on the error of the positional signal still remains although reduced in comparison with that of the Japanese Patent 3500328.